Quentin Stafford-Fraser's blog

If you’ve done any serious video work, you’ll know that European TV runs at 25 frames per second, essentially because early TVs used the frequency of the mains power supply, which is 50Hz, while in America, where the power is at 60Hz, TV runs at 30 frames per second.

Except that it doesn’t.

It actually runs at 29.97 FPS in the States. You don’t need to know this if you’re just creating YouTube videos, but is very important if you’re doing serious TV production and you don’t want your hour-long documentary to have the vital last 4 seconds chopped off. Over a day of TV programming, these little discrepancies all add up, so you need to get it right.

So, why 29.97?

Matt Parker has made a very nice little video explaining how that number came about.

Now, cinema film is generally shot at 24fps, which was chosen as a nice compromise between having smooth motion and not using too much film (or having to change film reels too often). It also makes for nice round numbers of frames if, say, you need to make something quarter of a second shorter by taking a razor blade to your footage.

However, in fact, movies no longer use that nice round number either! Why not? Well, when you want to broadcast movies on television, you do so via a process that involves converting two film frames into three TV frames, which again gives nice round numbers if you’re going from 24 to 30. (More info here.)

But we know that TV actually runs at 29.97 FPS, and as a result, most cinema film is actually recorded at 23.976 FPS, to make that conversion process still work smoothly.

So that’s where those funny numbers come from, in case you were wondering. You can now impress your friends in a pub trivia quiz…

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